Elevated serum melatonin levels during human late pregnancy and labour.

Melatonin (MLT) shows an influence on gonadal steroid genesis, and has soporific effects. Serum MLT levels were examined during late pregnancy and 4 days after delivery in 25 women. Circulating levels of melatonin were analysed as integrated values (areas under the curve [AUC]) over 24 hours, 5 to 2 days before and 4 days after delivery. Antepartum AUCs were significantly increased compared with postpartum AUCs. Additionally, MLT levels were measured every 2 hours in a subgroup of 11 women during spontaneous labour between 08.00 and 12.00 h at a time when physiological serum MLT levels were low. Increased MLT levels were determined and compared to MLT levels measured in a previous evaluation of the antepartum AUCs. Elevated serum MLT levels during late-pregnancy and labour may influence the concentration of receptors of gonadal steroids in the gravid uterus at term and the psychic perception of painful uterine contractions during labour.